The effect of milk proteins and curd on serum Angiotensin Converting Enzyme activity and lipid profile in Wistar rats

Abstract

Fermented milk and milk proteins have shown beneficiary health effects in humans. Angiotensin-II, which is formed from angiotensin-I by Angiotensin Converting Enzyme (ACE), plays a major role in regulating the blood pressure in humans and animals. Two experiments were carried out to determine the effects of prolonged consumption of milk proteins (casein & whey) in comparison with fermented milk (curd) on serum ACE activity and lipid profiles in Wistar rats.In experiment I, test groups were given 2 mL of hydrolysed casein or curd, whilst in experiment II, test groups received 2 mL whey and controls received 2 mL of water. The percentage differences obtained for individual animals were analysed after eight weeks. Casein hydrolysate fed group had a 4.3% reduction in serum ACE activity when compared with 3.5% reduction in curd hydrolysate fed group. The mean percentage difference of ACE showed significantly lower values (p<0.05) in both casein and curd fed group when compared with the control. A greater reduction in serum total cholesterol was noted in the curd fed group (7.3%) when compared with the whey fed group (5.4%) and the casein treated group (0.8%). The mean percentage difference was significant (p<0.05) only in the curd and whey treated groups. There was no significant difference in feed intake, body weight, serum high density lipoprotein cholesterol and triglycerides, between the treated groups and the control groups. This indicates that both casein and curd have the effect of lowering serum ACE activity.

Antihypertensive peptides from curd

“…Each curd sample was mixed well and subjected to sequential enzymatic digestion with pepsin, trypsin, and carboxypeptidase A at their optimum pH and temperature for 24 h.[ 3 ] Digested curd was centrifuged and filtrate obtained. Filtrate was subjected to reverse-phase HPLC (C18, silica column, Agilent 1200, DAD G1315B detector) separation at room temperature (30°C) using the same solvent gradient as whey.…”

“…The absorbance was recorded at 228 nm against a blank that had the inactive enzyme using an ultraviolet spectrophotometer. [ 3 ]…”

“…The protein fraction of milk is composed of 80% casein and the remaining 20% being whey proteins (α-lactalbumin, β-lactoglobulin and immunoglobulins). [ 3 ]…”

“…Studies have proven that fermented foods contain live bacteria that influence the chemical composition of the fermented product, especially milk proteins which result in short chain fatty acids. [ 3 ] Further short chain fatty acids such as acetic acid, propionic acid, and butyric acid have a feedback inhibition on the 3-hydroxy-3-methylglutaryl-coenzyme A reductase enzyme which regulates the rate-limiting step in cholesterol synthesis and reduces the serum cholesterol levels. [ 3 ] Reduction in serum cholesterol reduces the formation of atherosclerotic plaque.…”

“…[ 3 ] Further short chain fatty acids such as acetic acid, propionic acid, and butyric acid have a feedback inhibition on the 3-hydroxy-3-methylglutaryl-coenzyme A reductase enzyme which regulates the rate-limiting step in cholesterol synthesis and reduces the serum cholesterol levels. [ 3 ] Reduction in serum cholesterol reduces the formation of atherosclerotic plaque. Not only fermented milk, other proteins such as soy proteins also have cholesterol-lowering effect.…”